Welloilbeefhooked

iTrader: (3)

Hello all,

As I like to drive my Impreza and not worry about the costs of the fuel I decided to LPG it.

It's not really a working project as such, more a look back at the process of fitting the kit.

I have started putting together a site to document the process and any ongoing problems/issues. Anyone got a spare engine??!!

If anyone here fancies making it look a bit more presentable please let me know as I am no web site designer!

Scooby LPG

Any thoughts, comments or questions are welcome.

Cheers,

Wayne.

minty

iTrader: (1)

That looks very interesting, how's the car performing, is it getting hot at all engine temps i mean?

Cheers
Chris.

Welloilbeefhooked

iTrader: (3)

Chris,

No increase in engine temps. I don't monitor oil temps but the water is the same as its always been at 87c. The vaporiser unit sucks alot of heat when converting liquid to gas.

Performance wise its not too far from petrol performance. I regapped the plugs from .65mm to .55mm and that made a big difference on boost at 1bar.

I'm running 1 bar purely on LPG and it switches back to petrol at 1.4 bar without any issues. I know that there "could" be issues with valve seats but thats something I can rectify IF I have any problems.

Also, just found out how to start it on LPG without petrol which helps economy on cold starts. As long as you don't go crazy it doesn't freeze the vaporiser which is a common cold start problem.

So far so good.


Wayne.

Jolly Green Monster

iTrader: (4)

you got my interest and considering converting my daily runner next month or two

Welloilbeefhooked

iTrader: (3)

Simon,

I will post the following on the website sometime soon, but thought this may be worth reading.

I get 19mpg on LPG when used for motorway and local driving. Not driving too hard but on boost when away from the M1. Petrol returns 24-25 under the same conditions.

For 1300 miles I spent £178 in total which includes £30 of V-Power. If this had been simply V-Power it would been £274!! for the same number of litres Thats a £96 saving in one month. So in 9 months it has paid for itself.

I'm still using some V-Power as at 1.4 bar (or above 3.5k AND 16ms inj) it switches back to petrol. Its seemless to be honest and I have checked this using the LED I have placed across one of the petrol injectors.

If you are ever in Yorkshire and want to have a look or drive it, let me know.

Wayne.

Jolly Green Monster

iTrader: (4)

cool.. I do 2tanks a week at least... last two weeks I have done 4tanks each!

you going to sso?

just need to get my other scoob on the road so I can install on current one

Simon

Green Classic 98

Wayne,

Good to see your site about the conversion, especially with the mpg figures, if my sums are right, after the cost of the initial installation, cost wise its like getting the equivilent of 36 "mpg" on vpower. Very impressive for the cars spec. A couple of questions:

o I presume the road tax you have to pay stays the same?

o How is the number plate held on , is it on a sprung loaded hinge or something?

o Was there an option to replace the existing fuel tank with a gas tank, and put a small petrol tank somewhere else?

o Did you consider a higher compression ratio option (instead of LPG) to improve the mpg (perhaps with aquamist or methanol to prevent detonation)?

Welloilbeefhooked

iTrader: (3)

The MPG should be 2 x 19mpg = 38MPG as LPG is 54p and V-Power 108/9p?

Anyway, The road tax stays the same as it's pre 2001. No discount at all. In saying that, 2001 onwards and you would only save £15 per annum anyway.

Numberplate is held on 2 hinges and then the trusty old velcro at the bottom. I am looking into some new fasteners as this was just a quick fix option.

Fuel tank could easily be fiited in the spare wheel well and you can keep the boot space. However, the tanks are limited in their capacity to around 60litres (fill to 80% only, so 48 litres). As far as I am aware you can't get a tank to fit where the scoobs tank is. It has to be a cylidrical tank of some description due to the 140psi pressure. My tank holds 64 litres of LPG, hence the decision to have the tank I have. I fill up a little more than once a week as it is.

The point you make about the compression ratio is interesting. I didn't consider that pre fit, but have now seen alot of info about raising the compresion ratio to run on LPG. LPG should benefit from higher compression ratios, although thats not a good thing IF you are running a dual fuel system and still using petrol. Some people, especially taxi drivers use ONLY LPG and nothing else. Not sure if they have removed everything petrol related though. By all accounts only a handful of people have modified there compression ratio to take the LPG into account. I suppose this is because its seen by most people as an economy fuel.
Last point to mention about the power, even if you did raise the compression, is that LPG only has around 85% the calorific value of petrol and even though it has well over 100 ron ratings (I think its about 105-6) it just isn't a performance fuel.

Wayne.

Welloilbeefhooked

iTrader: (3)

Simon,

When is sso? I may come along although it depends on other factors.

Wayne.

Green Classic 98

Wayne,

Your math is better than mine . Wow, it just gets better -cost equivilent of 38 mpg eh!

Thanks for the indepth info, I have read that a each increment in CR (e.g. from 8:1 to 9:1 etc) should result in a 3% increase in power on a normally aspirated engine, (e.g. like a scooby off boost) my guess is that you get a similar or greater power increase whilst on boost (assuming you don't get det).

If you can get more power (by raising the CR) for the same amount of fuel/air input you have made the engine more efficient and you should better mpg. Off boost you would get better pickup and improved mpg.

Typically scoobs run an 8:1 cr and achieve about 25mpg combined, whilst Audi A3 Turbo's run a 9.5:1 and acheive about 31mpg combined. So I would guess you could take a scoob to 9.5:1 without too many problems as long as it was mapped accordingly (I read that some tuners already do this - e.g. RCM(?)) I also read some place that when you reach the CR boundaries that each additional 6 octane is good for an increase of 1 increment in CR (e.g. 9.5:1 to 10.5:1?) (again normally aspirated engines).

I don't know if the calorific value of diesel is less or more than VPOWER? Either way, I think diesels do such good mpg mainly due to there very high compression ratios, upto 25:1 normally aspirated, 18:1 on turbos.

Dave

Welloilbeefhooked

iTrader: (3)

Dave,

You are a sod!! You have me thinking about a possible new engine now!!


Simon,

What your thoughts on the CR? I was thinking about building another engine soon.

2.0 CDB if I can get one.
Decent rod and pistons
STI V4 heads
New crank and the rest.

What sort of CR could I run considering the 2 fuels that would be used?

I suppose if LPG only was to be used (which is programmable in my ECU via the engineers key) then a higher CR would be do-able. Although boost may have to be dropped?

Also, JFYI, quite a few people in OZ are using the megasquirt? ECU to run the LPG system.
Once you have the gas pressure set you can map as you would a petrol engine. You would only have to control the two gas shut of valves via some sort of switch. Gas temp may be an issue.
Wayne.

Green Classic 98

Wayne,

Damn, you sussed me! Free R&D for my next motor! Thought I was going to have to buy a diesel rep mobile, but now can justify another scoob. Keep up the good work

On a different tack to increasing CR, if the LPG kit does not have its own ignition timing map (?), you are not making the most of the increased octane of the LPG, you could get a remap on petrol plus 10% methanol and have more power/mpg on the LPG as the timming would be more optimal... Day to day you would not need much methanol as you will mainly be running on LPG...

Welloilbeefhooked

iTrader: (3)

Good idea. I have started mapping my Power FC to generate an LPG map. I can increase the timing quite alot (10 deg extra at 1 bar) and it makes some difference but an increase of around 4 deg seems to feel better. I haven't logged anything yet but may if I get the time. The commander I have fitted in the dash allows a global timing adjustment which I have used a time or two just to see what the car feels like. Going past the 4 degree mark makes the boost feel "soft" if that makes sense.

Quite a few of the V8 boys use a device that switches the advance curve when on LPG. Apparently more advance at lower RPM and LESS at higher RPM.

I will have to find out why that is.

Wayne.

Jolly Green Monster

iTrader: (4)

sso is 25th may

you can gain some of the compression effect or rather higher ron by running more ignition...

you still have to remember it is running a turbo so I would stick to sensible compression 8:1 to 8.25:1 ish.. I am assuming you are crossing the line between lpg compression and turbo engine compression?

Simon

Jolly Green Monster

iTrader: (4)

if the ron is 105/106ron you could be going past the most best timing.. hence loosing power.. worth playing on a dyno..

also consider the effects on the fueling both ignition and lpg wise.

I presume the lpg ecu is just running same injector pulse width as the petrol injectors? you just bought similar size lpg injectors as the petrol ones?
surely this maybe your mpg decrease on the lpg? if it has less calorific value then you maybe using more throttle to get to cruise speed also of course.

I presume the lambda is still working and stoich of lpg is similar to petrol?
info like that may allow more mpg on the lpg by switching closed loop lambda off and retuning it.. or does the lpg ecu alter the lambda signal?

Simon

Green Classic 98

Of course, agree with Simon, increased timing makes sense upto a point, beyond that point, the force of combustion is too early on the piston and tries to push the piston down (a bit) when its just finishing the compression stroke. (IMO the fact that you are able to advance your timing this far, could be demonstrating that you could be running a higher CR to make the most of the higher octane rating of the LPG, of course this will be different at high boost).

Jolly Green Monster

iTrader: (4)

agreed but at 1bar only at the moment..

is there enough headroom in lpg injectors to go to 1.4bar? assuming still they are similar to petrol injectors in size?

Green Classic 98

"Quite a few of the V8 boys use a device that switches the advance curve when on LPG. Apparently more advance at lower RPM and LESS at higher RPM."

"LESS at higher RPM", good question, do they mean a lot more advance at low RPM and a little more at high RPM or do they mean negative at higher RPM compared to the base map...

Jolly Green Monster

iTrader: (4)

wonder also if that is for safety rather than necessarily the best method, with powerfc on there you can monitor knock (preferably with cans too) and monitor power output on a dyno etc and alter each cell in map etc

perhaps egt would be good to monitor

Simon

Welloilbeefhooked

iTrader: (3)

Simon,

Just getting an EGT sensor and 0-5v adapter kit for the datalogit as we speak. Its going in the headers in the OE Lambda location for the early cars.

Just to clarify about the gas ecu and injectors. The petrol ECU runs as it does on petrol and the gas ECU simply breaks the wires to each petrol injector, therefore switching them off when on LPG.

The gas ECU then runs the new LPG injectors by itself and injects the correct amount of LPG to match the petrol that would have gone in. So on boost if my AFR should be 11.5:1 the gas is injected so that I still see a petrol AFR of 11.5:1 The injectors dont have to be the same size as the petrol ones as a self calibration of the gas ECU sorts everything out. All you have to do after that is alter an 8 point curve for LPG fueling.

As we know 14.7:1 is Lambda of 1 for petrol. LPG is 15.8:1 for Lambda of 1.

So when I run LPG the LC-1 I have still shows 14.7:1 (the petrol setting) even though its actaully 15.8:1 LPG. As you probably know this is due to the setting within the LC-1.

So in short, whatever AFR it was running on petrol will be matched by LPG although the gas ECU DOESN'T monitor the Lambda sensor at all.

More throttle is definately required to get the same vehicle speed. This is demonstrated when switching from gas to petrol at a constant speed. The speed increases slightly at the same throttle opening.

I have tried 1.4 bar boost and it cut back to petrol instantly. That was with the gas pressure at 1.2 bar. I have since raised the gas pressure to 1.4 bar and it now runs at 1.4 bar boost on gas. So it was down to maxing out the injectors. The pressure can be raised to a max of 1.6 bar with the vaporiser I have.

At petrol injector times of 18ms the LPG injectors are around 24ms.

The 1.4bar boost region is where I want to monitor the EGTs to see if it is indeed higher than when on petrol.

Wayne.

Jolly Green Monster

iTrader: (4)

that is not possible... it must be using the same pulse width, unless the injectors are matched size with afr offset taken into account it will just be running a guessed afr.

altering the pressure will richen the whole lot up

is the lpg ecu programmable?

Simon

Hol

iTrader: (1)

Im sure Simon can confrm it, but my 1999 Forester has a higher compression engine out-of-the-box, than the same year Impreza equivalent.


I could be talkin bobbins though!!

Welloilbeefhooked

iTrader: (3)

Simon, it users the lambda only when calibrating. I will post a pic later to show both gas and petrol inj times at the same time. My logs show the afr is too close to tell the difference so it must be a very clever ecu.

Wayne

Green Classic 98

Wayne

Just been looking on the dark side, says on the Mitsubishi UK site that the EVO X has a 9:1 CR, they sell a 360BHP HKS tuned version with this CR, so its appears that it can be done (even on pump fuel). Considering that LPG has a higher octane rating and so would petrol with 10% methanol I GUESS 9.5:1 might be ok (best to spec any new engine with a thin head gasket, if there were problems you could always convert to a thicker head gasket to reduce the compression ratio (I think Cosmetic make two thicknesses...), or use water injection (even more complexity, and it might not be reliable enough...))

If you did dare to try this, you might also try to find pistons with a similar shape to A3 Turbos or EVO X (and no, I have no idea what these look like!).

===================================

Simon

I wondered if you, or any tuners you know, had the chance to map any scoobs with 9:1 CRs or above? Does anyone out there already run these sort of CRs successfully on a tuned Scoob?

Also, I think I read that you may have had an aquamist system on your car in the past? If you did, do you still have one installed, has it been reliable?

=================================

I have spoken to a guy who had a 2.0l with a 2.5 crank that ran 11.5:1. The guy obviously struggled to get any boost into it without det. He then installed aquamist, which improved matters (but I don't know how much - I will try to find out). One day the water injection failed (may be it ran out of water or a jet blocked or something) and it melted a piston. So its probably more reliable to use LPG or methanol in the petrol when running higher CRs.

Dave

Jolly Green Monster

iTrader: (4)

okay.. sounds like I need my own to play with

Jolly Green Monster

iTrader: (4)

highest knowing was around 8.5:1 roughly.. spooled nice and wouldn't take much ignition but still felt quick.. but no resilence to det so had to be careful with advance as it was sensitive to fuel etc

although related you have to be careful comparing flat4 engine etc

Simon

Jolly Green Monster

iTrader: (4)

yes believe that is correct, also lower rpm limit

Welloilbeefhooked

iTrader: (3)

I thought it was about time for an update on this project.

The rumours about the platinum spark plugs burning out when using LPG don't seem to apply to my car. The plugs look like new and the gaps remain the same at around 0.6mm.

I seem to have the flashlube set to use 1ml for every litre of LPG and this equates to 8 drops per minute at idle.

I have since raised the LPG gas pressure at the injectors to 1.5 bar and this provides better switching to petrol at higher rpm.

Talking of higher rpm and boost, I have now got the car running 1.4bar boost on LPG WITH an additional 4ms of petrol over normal. This results in richer AFR's at WOT (11.8 -11.2 standard, 10.8 ish with LPG). The car runs fine and seems to be ok, although I will have an EGT gauge inside the car by next week.

Been for the MOT recently and it flew through.

CO should be less than 3.50 [% Vol] and is 2.03

HC should be less than 1200 [ppm Vol] and is 280

The tester only lets tghe car idle to do the test. Non of this fast running stuff. They also told me that they test the car on whatever it is running on when the test starts. So one year it can pass on LPG and the next, petrol.

After tweaking the LPG map, if you can call it a map, I am now able to get 21MPG on LPG, so the equivalent of 42 on petrol.

Not had the time to get the website updated, but have taken some screen shots of the setup within the ECU.

satpink

iTrader: (9)

what a brilliant read, i would love to have my scoob on lpg, what kind of costs are involved?

satpink

iTrader: (9)

must be a lot